Ball and socket joint for interconnecting a ceramic roller to a bearing

Abstract: A ceramic roller, comprised of a shell (2) and a shaft (1) passing through the shell (2), characterized by at least one ball-and-socket joint between the shell and the shaft. At least one end cap (3,4) is placed at an end of the shell (2) and mounted on the shaft (1). A ball-and-socket joint (8) is provided between the shell (2) and the end caps (3,4) or between the shaft and the end caps. The ball-and-socket joint (8) is preferably obtained by the provision of an annular collar having a rounded cross section (9,12) mounted between the truncated conical bearing surface (6) of the shell (2) and the end caps (3,4).

Description: Background Of The Invention The invention generally concerns a roller mounted on bearings, and is specifically concerned with a ball and socket joint between a ceramic roller and the bearings for eliminating localized stresses that can cause the roller to chip. Rollers designed to support loads such as a metal strip in a heat-treatment furnace in which the strip is to be annealed at a relatively high temperature are already known. Such rollers are comprised of a cylinder of ceramic refractory material. An end cap mounted rotatably on a bearing is fixed at each end of the ceramic cylinder. U.S. patent 4,399,598 describes a ceramic roller for transporting glass sheets through a heat treatment. The cylinder is mounted rotatably on bearings by means of end caps mounted with play at each end of the cylinder. One or more radially compressible split metal rings are placed in the space between the outside diameter of the cylinder and the inside diameter of the end cap. A roller of similar type is also disclosed in U.S. patent 4,404,011; it is comprised of a cylinder of refractory material at the ends to which metallic end caps are fixed. Play is provided between the end caps and the cylinder. Flat leaf springs are placed around the periphery of this play. These known systems of the prior art make it possible to take up the differential expansion between the roller and the end caps when the roller is exposed to heat. When heated, the cylinder of refractory material expands practically not at all while, on the other hand, the metallic end caps expand greatly. The play between the cylinder and the end caps consequently varies substantially as a function of the temperature. This is why it is necessary to provide resilient devices in this space that prevent backlash from occurring between the end caps and roller over a broad range of temperature. However, these prior art systems have the shortcoming of not assuring coaxiality between the end caps and the cylinder under load. In effect, when the cylinder supports 1 load, the resilient devices, whether involving the split rings disclosed in U.S. patent 4,399,598 or the leaf springs of U.S. patent 4,404,011, are deformed such that the end caps are displaced angularly with respect to the axis of the cylinder, thus causing the cylinder of the roller to rotate eccentrically with respect to the bearings. To remedy these disadvantages, a roller corresponding to the entering clause of claim 1 or claim 9 having an end cap with a conical joint was developed as shown in U.S. patent 5,096,051 (EP-A- 0 419 300). It is comprised of a ceramic cylinder, e.g., a vitreous fused silica, at the end of which at least one end cap is mounted. The junction between the cylinder and the end cap is a conical connection. The cylinder can be solid or comprised of a shell traversed by a metal shaft. In this latter case the end caps are mounted on the metal shaft, at least one of the end caps being applied resiliently (e.g., by means of helicoidal springs) against one end of the shell. A roller of this type remedies the disadvantages associated with the prior art and assures coaxiality of the cylinder and the end caps under load. This coaxiality is not affected when even an elevated load is applied on the roller. Nevertheless, a device of this type also presents a number of shortcomings. In theory, the contact between the end caps and the cylinder (solid or hollow) is made along a frustroconical area, i.e., the conical engagement area of the roller ends on the conical surfaces of the end caps. In practice, because the conical surfaces of the cylinder and the end caps cannot be perfectly complementary due to machining tolerances, the contact is made only along an elongated zone on all sides of a contact generatrix. This contact zone rotates around the circumference of the cylinder-end cap interface with the rotation of the roller. In other words, when the roller turns, the contact between the end caps and the ends of the cylinder is progressively made over the entire periphery of the circumference of the interface. The metal shaft is deformed under load. Consequently, the contact zone, already reduced to an elongated zone located along the generatrix due to machining tolerances, is transformed into a zone of point support. The contact pressure between the end caps and the roller then increases considerably until it exceeds that admissible limit for the ceramic forming the cylinder. This then leads to a chipping and/or fissuring of the ceramic. The document 2 203 199 discloses a running wheel mounted on two ball bearings. It has two bearing supports having a spherical external surface which allows to spherically articulate the running wheel about its axle. Summary Of The Invention The object of the present invention is a roller designed in a non-limiting manner for applications in the glass or metallurgical industries which remedies the shortcomings of the prior art. The roller of the invention preserves a sufficient contact surface between the end caps and the cylindrical shell (or solid roller) despite the inevitable flexing of the shaft under load. A sufficient contact surface is understood to be a surface that is large enough so that the contact pressure between the materials never exceeds an admissible limiting value. Fissuring of the material constituting the shell, e.g., a ceramic material, is thus avoided ; therefore, the service life of the installation is greatly increased. These goals are achieved with a roller according to claim 1 or claim 9 wherein an essentially spherical joint is provided at each end of the shell between the bearing surface of the shell and the bearing surface of each end cap or between the shaft and the end caps for allowing deflection of the shell under load. Thanks to the spherical interface of the ball-and-socket joint, the area of the contact zone between the cylindrical shell and the end caps is not reduced when the shaft flexes under load. Likewise, no supplementary flexing load is imposed on the roller. According to one embodiment, the shell is hollow and a shaft passes through said shell, one end cap being fixedly mounted on said shaft, the other end cap being slidingly mounted on the shaft, the roller further comprising resilient means for pressing the slidable end cap against the bearing surface of said shell. According to another embodiment, one end cap is fixeldy mounted on a shaft and the other of said end caps is slidably mounted on a shaft, the roller further comprising resilient means for pressing the slidable end cap against the bearing surface of said shell. The ball-and-socket joint or globe-and-socket joint may be provided between the ends of the cylindrical shell and the end caps. In a second embodiment, the ball-and-socket joint can be provided between the shaft passing through the cylindrical shell and one or both of the end caps. In a third embodiment, the ball-and-socket joint is obtained by mounting an intermediate piece on a bearing surface, e.g., conical, of the shell between the shell and the end caps. This piece preferably has a small width and thickness relative to its diameter. Other features and advantages of the present invention will become evident in reading the following description with reference to the attached Figures. Brief Description Of the Several Drawings Figure 1 is a partially cutaway schematic representation of a known prior art roller ; Figure 2 illustrates the contact zone between the shell and an end cap in the case of a roller of the type shown in Figure 1 ; Figure 3 is a partial cutaway view of a first embodiment of a roller according to the invention; Figures 4, 5, and 6 are partial cutaway views of other embodiments of the present invention; Figure 7 is a perspective schematic perspective view that illustrates the contact zone between the shell and an end cap in the roller of the invention; Figure 8 is a partial cutaway view of still another embodiment in which the ball-and-socket joint is placed between the end cap and the shaft, and Figure 9 illustrates another embodiment of the invention in which the cylindrical shell is solid. Detailed Description Of The Preferred Embodiment Reference 1 designates a shaft in Figure 1. It passes through a generally cylindrical shell 2 of refractory material, e.g., a ceramic. An end cap, e.g., of metal 3 is mounted at one end of the shell 2. A second end cap 4 is mounted at the other end of the shell 2. In this prior art roller the end cap 3 is mounted fixed on the shaft. The end cap 4 is slidably mounted on the shaft 1 and a helicoidal spring 5 biases it against the shell 2 (in Figure 1 the shell and the two end caps are shown spaced apart for better visibility of the components). The shell 2 has a truncated conical surface 6 at each of its ends while the end caps 3 and 4 have a truncated conical surface 7, the conicity angle of which is equal to that of surface 6. The conicity angle is preferably relatively large in order to avoid the phenomena of jamming or binding of the male cone (of the shell) in the female cone (of the end caps 3 and 4). This angle depends on the coefficients of friction of the materials present. For example, it could be an angle of about 70° for a steel/vitreous fused silica interface. This roller is accompanied by the shortcomings mentioned above, i.e., the fact that the contact zone between each of the end caps 3 and 4 and the shell 2 is reduced almost to a point zone when the shaft 1 flexes under load. The contact surface zone between the shell (or a solid roller) and an end cap in the case of the Figure 1 prior art roller is shown in Figure 2. It is evident that this zone 17, of small width, is distributed on all sides of a generatrix of the truncated conical surface 6 of the shell 2. This arises from the fact that the diameter of the truncated conical part of the shell 2 is necessarily slightly less than the internal diameter of the end caps 3 and 4 (not shown in figure 2) and also from the fact that the end cap is deformed very little because it is solid. It is understood that a slight defect in alignment of the end cap with respect to the roller sharply reduces the area of the contact zone 17 to a point zone. Figure 3 shows a roller according to the invention that makes it possible to remedy the shortcomings of the roller described in reference to Figure 1. The pieces numbered from 1 to 7 are identically present. However, the end caps 3 and 4 are modified to present spherical bearing surfaces 8 instead of truncated conical surfaces 7. The presence of an intermediate piece 9 placed between the shell 2 and each of the end caps 3 and 4 is also noted. Each of the pieces 9 have the form of a collar or ring. The face of the pieces turned toward the end caps 3 and 4 has a spherical bearing surface of the same radius of sphericity as the surfaces 8 of the end caps 3 and 4. The faces of the pieces 9 directed toward the shell 2 have a truncated conical bearing surface of the same conicity as the surfaces 6 of the shell 2. The centers of the ball-and-socket joints are spaced in order to define a precise position of the axis of the roller. When the shaft 1 flexes under load, the area of the contact zone between the intermediate piece 9 and the spherical bearing surface 8 of the end caps 3 and 4 is displaced so as to maintain the area of the contact zone surface constant. Figures 4 through 6 illustrate other embodiments of the invention. In Figure 4 there is no intermediate piece 9 between the end caps and the shell. A spherical bearing surface 11 is formed directly on the shell 2. In Figure 5 an intermediate piece 12 is provided that has truncated conical and spherical faces reversed relative to piece 9. Its truncated conical face is directed toward the end caps 3 and 4 while the spherical face is directed toward the shell 2. The intermediate pieces 9, 12 have a small width and thickness relative to their diameters. This facilitates changing the orientation of the contact zone. In effect, because the intermediate piece has a small width, it can be readily deformed elastically to adapt to the contour of the end of the shell. The intermediate piece 9, 12 is preferably of a material having a good coefficient of metal/metal friction, e.g., copper. Figure 7 shows the bearing surface zone (or contact zone) 19 of the shell 2 (or of a solid roller) on an end cap in the case of a roller according to the invention, in particular in the case of the use of an intermediate piece such as 9, 12. Zone 19 is distributed along an arc of a straight section of the truncated conical part 6 of the shell 2 through a plane perpendicular to the longitudinal axis of the roller. This arc of a circle is defined by an angle α originating at the axis of rotation of the cylindrical shell. The value of the angle α depends on the flexibility of the intermediate piece 9, 12. Given that the width and thickness of such a piece are relatively small, it is deformed under load and conforms to the shape of the shell along an arc subtending an angle α. It is assumed that in the case of a variation in alignment between the end cap and the shell, the surface of the contact zone 19 is reduced very little. Given that the contact zone does not decrease when the shaft 1 flexes under load, as is the case in the prior art, it is no longer necessary to over-dimension the thickness of the shell to compensate for point contact stresses. A decrease in the weight of the latter results. Due to the reduction in thickness of the shell 2, the support surface 10 of the end caps 3, 4 on the shaft 1 can be readily distributed on both sides of the plane of application of the load exerted on the end caps 3, 4 i.e., the weight of the shell 2 itself, augmented by the load transported by the latter. The jamming or clamping effect that could be observed in the prior art due to an uncertain support is thus avoided. Figure 8 shows another embodiment in which the ball-and-socket joint is obtained not between the shell and the end cap, but between the end cap and the shaft 1. A ring 20 is mounted on the shaft 1 for this. It has a spherical surface 22. The center of the sphere is located on the longitudinal axis 24 of the shaft 1. The end cap 4 can thus pivot around the center O, effecting a ball-and-socket joint. Figure 6 shows a variation of the invention in which the ball-and socket joint is obtained by a spherical surface 15 formed on the shell, supported on a truncated conical surface 16 of the end cap. Figure 9 shows a final embodiment in which the shell 2 is solid and not hollow. Consequently, there is no shaft passing through such as the shaft 1 shown in Figures 1 through 8. Instead, each end cap 3, 4 is mounted on a shaft 1a, 1b. The end cap 3 is fixedly mounted on the shaft 1a. The end cap 4 is slidably mounted on the shaft 1b. It is forcefully engaged against the shell 2 by a spring 5.

Claims: A roller comprised of an elongated shell (2) of refractory material and being adapted to be mounted rotatably, said shell (2) having two ends, a bearing surface (6, 11, 15) being defined at each end of the shell (2) ; an end cap (3, 4) mounted at each end of said ends of the shell (2), each end cap (3, 4) having a bearing surface (8, 16) for receiving a bearing surface (6, 11, 15) of the shell (2), these end caps (3, 4) being of a material having a higher coefficient of expansion than that of the refractory material of the shell (2), characterized in that an essentially spherical joint is provided at each end of the shell (2) between the bearing surface (6, 11, 15) of the shell and the bearing surface (8, 16) of each end cap (3, 4) for allowing deflection of the shell (2) under load. A roller according to claim 1 wherein said shell (2) is hollow and a shaft (1) passes through said shell (2), one end cap (3) being fixedly mounted on said shaft (1), the other end cap (4) being slidingly mounted on the shaft (2), the roller further comprising resilient means(5) for pressing the slidable end cap (4) against the bearing surface (6, 11, 15) of the shell (2). A roller according to claim 1 wherein one end cap (3) is fixeldy mounted on a shaft (1a) and the other (4) of said end caps is slidably mounted on a shaft (1b), the roller further comprising resilient means (5) for pressing the slidable end cap (4) against the bearing surface (6, 11, 15) of said shell (2). A roller according to any of claims 1 to 3, wherein at least one spherical joint includes an intermediate piece (9, 12) mounted on a bearing surface of the shell (10, 11), and placed between the shell (2) and an end cap (3, 4). A roller according to claim 4, wherein said at least one intermediate piece (12) has a spherical surface that is supported on a bearing surface (11) of the shell (2). A roller according to claim 4, wherein said at least one intermediate piece (9) has a spherical surface that is supported on a spherical bearing surface (8) of an end cap. A roller according to any of claims 4-6, wherein said at least one intermediate piece (9, 12) is made of copper. A roller according to any of claims 4-7, wherein said at least one intermediate piece (9, 12) is a ring or collar of small width and thickness relative to its diameter. A roller comprised of an elongated hollow shell (2) of refractory material and being adapted to be mounted rotatably, said shell (2) having two ends, a bearing surface (6, 11, 15) being defined at each end of the shell (2) ; a shaft (1) passing through said shell (2) ; an end cap (3, 4) mounted at each end of said ends of the shell (2), each end cap (3, 4) having a bearing surface (8, 16) for receiving the bearing surface (6, 11, 15) of the shell (2), these end caps (3, 4) being of a material having a higher coefficient of expansion than that of the refractory material of the shell (2) ; one end cap (3) being fixedly mounted on said shaft (1), the other end cap (4) being slidingly mounted on the shaft (2), the roller further comprising resilient means(5) For pressing the slidable end cap (4) against the bearing surface (6, 11, 15) of the shell (2), characterized in that an essentially spherical joint is provided at each end of the shell (2) between the shaft and the end caps (3, 4) for allowing deflection of the shell (2) under load.

Inventors: GAUTIER DAVID, GAUTIER, DAVID
Applicants: VESUVIUS FRANCE SA, VESUVIUS FRANCE S.A.
Application year: 1994
Main classification: B65G39
IPC codes: F16C13, F16C11, C21D1, B65G39